Cancer of the prostate is the second most common cancer in men and the third leading cancer killer. The etiology of the disease is unknown. However, it is singularly absent in castrates, and many tumors retain the property of androgen dependence similar to normal differentiated prostate tissue. Recent studies suggest that androgen receptor proteins may be involved in the mechanism by which these responses are regulated. However, there are complicating reports concerning altered receptor levels associated with prostate cancer. Clearly there is a need for a more reliabe and specific means for studying receptors in tumor tissue. An antibody to the receptor molecule would provide a reliable probe for measuring receptor content in cancer tissue. We have recently developed the necessary techniques for purifying the androgen receptor to apparent homogeneity from steer seminal vesicle. These techniques include both differential binding to DNA-Sepharose and testosterone-affinity chromatography. In this proposal we plan to utilize similar techniques to purify the androgen receptor from the Dunning R3327 tumor. We will raise antibodies tothe receptor protein and use immunocytochemical techniques for localizing the androgen receptor in tumor tissue slices. These procedures may lead to a method for testing routinely for the presence of androgen receptors in biopsies from human prostate tumors.